The present invention relates to a brake system for automotive vehicles with an actuating unit including a pneumatic brake power booster and a master brake cylinder connected downstream of the booster and connected to wheel brakes, wherein a control valve of the brake power booster is operable irrespective of the driver's wish by a solenoid having an armature that is in force-transmitting connection with one of the sealing seats of the control valve, a deceleration controller to which a signal representative of the vehicle deceleration is sent as an input quantity, wherein the output quantity of the controller influences the position of the control valve and is compared in a first summer with a signal representative of the actual condition of the control valve, and the control difference representative of the result of the comparison is sent to a position controller, which influences the position of the control valve, and the output quantity of which corresponds to an electric current to be supplied to the solenoid.
International patent application WO 95/03196 discloses a brake system of this type. The control difference between a deceleration wish signal and an actual deceleration signal, which corresponds to a quantity proportional to the brake force (brake force nominal or actual value), is sent as an input quantity to the deceleration controller of the above mentioned prior art brake system. In particular the braking pressure, the pressure differential acting in the pneumatic brake power booster, or the rotational speed of at least one vehicle wheel may be used as possible physical parameters. In response to the physical parameter chosen, the deceleration controller is configured as a braking pressure controller, pneumatic differential pressure controller, or wheel deceleration controller. Corresponding to the control difference and the demanded nominal value gradient, the deceleration controller calculates the desired position for the armature of the solenoid which directly influences the opening condition of the control valve of the brake power booster.
The output signals of the deceleration controller, in consideration of sensed actual values for the armature position and the current supplied to the solenoid, are further processed in a position controller having an output quantity which represents the control quantity for actuating the solenoid.
In particular the following problems occur in the state of the art position control of the solenoid:
1. A statically non-linear system performance of the solenoid, which is due to the non-linear progressive interrelation between the magnetic force and the process parameters `magnetic current` and `armature position`. This means a structurally inherent instability for the solenoid. PA1 2. In general, a high degree of dynamics and a weak system damping. PA1 3. The force which counteracts the solenoid upon actuation of the control valve (control valve characteristic curve) is non-linear to a great degree and, in addition, responsive to position and vacuum. After the control valve is opened, the counterforce will be reduced to such an extent as to exert an additional destabilizing effect on the solenoid. PA1 great amount of rigidity PA1 high degree of dynamics (characteristic values of the controlled system&lt;1 msec) PA1 low cost PA1 small mounting space for the installation of the control electronics directly on the brake power booster PA1 high malfunction resistance.